Your best option is to say nothing, and talk about your strengths rather than weaknesses. Most students have weaknesses, whether it's low grades in some courses or something else. Admission committees know that it's rare to get a student with no flaws, so what's important is whether the student's strengths are worth tolerating those flaws.
This is assuming you're not applying to the very top programs. There, bad grades in a fundamental course are unlikely to fly, unless you have some truly amazing accomplishments to balance it out.
Your plan of excusing the bad grades by citing lecturer incompetence is a bad idea. There are too many students who do poorly in a course and blame the instructor. There's no way to know whether you are one of those. Other students agreeing with you means little: Most students are not good enough for PhD programs, hence a minority of applicants get admitted. Besides, the committee is not going to canvas your classmates or look up your teachers on ratemyprofessors.com, they'll just throw your application in the bottom of the pile, and see if they can find a less complicated application. Moreover, some may very well feel that you should have found a way to teach yourself the topic regardless of poor instruction (such as reading the textbook) - in research, one often must learn things without any instruction at all.
If your grades in statistics are truly bad, I would recommend not applying to PhD programs in statistics right now. This by itself is a very strong reason not to admit you and no amount of skillful rhetoric in the application will save you. If it sounds unfair, it is - students from grade inflated schools absolutely have an advantage over others, but such is life. If you try to apply anyway, you will be fighting an uphill battle. I recommend delaying your application and taking some steps first to even the odds a little:
- Do an internship, get a job, or find some other way to obtain experience that will make you seem impressive to the program you're applying for regardless of grades - typically you want something where you get research experience, ideally with publication authorship
- Do a project or take a more advanced course in statistics and do really well, which would show that your understanding of statistics is strong in spite of bad grades in lower level courses - this would be the best way of "excusing" your earlier poor grades
You'd have to separately research what specific topics would impress PhD programs in your field. Usually some kind of short program can tick a lot of the boxes, such as a Master's Degree, or working in a research group. You'd lose 1-2 years but end up qualifying for a much better PhD program.